Aluminum plunger piston with thermal expansion regulating strip, for internal combustion engines

Abstract

In a plunger piston for internal combustion engines, having a regulating strip in the piston body, the regulating strip is arranged in the axial middle third of the height of the piston body and the regulating effect is designed so that the piston body possesses its narrowest installation play uniformly at the level of the regulating strip equally in the cold installation state and in the engine operation. Above and below this region with minimum installation play the piston body possesses spherically retracted end regions at its upper and lower ends for the generation of hydrodynamic lubricant oil wedges.

We claim: 
     
       1. In an aluminum plunger piston for internal combustion engines, comprising a piston head provided with grooves to accommodate piston rings, a skirt formed integral therewith having an outer bearing surface axially spaced from the piston head, and bosses through which bores are formed to receive a gudgeon pin, the improvement comprising (a) at least one horizontally extending thermal expansion regulating strip is located at each of inner surfaces of the skirt extending circumferentially between the boss bores, being spaced from one another and lying entirely within a region consisting of an axially middle third of the skirt in thrust and anti-thrust regions of the skirt,   (b) the outer bearing surface of the piston skirt is reduced in diameter at its ends in each case gradually over an axial length of 5 to 10% of a predetermined maximum diameter of the piston so that the skirt is substantially barrel-shaped, a remaining portion of the skirt lying axially between the reduced skirt ends having an axial dimension of 5 to 30% of the maximum piston diameter, and   (c) a portion of the skirt lying axially between the reduced skirt ends comprises maximum skirt external diameter in circumferential regions adjacent a plane of oscillation of a connecting rod at right-angles to the bore axis when a uniform temperature of the piston has risen to about 150 degrees C., whereby in use within a cylinder bore a clearance between the reduced ends of the skirt and a wall of the cylinder bore is greater than that between the bearing surface and the cylinder bore wall under all operating conditions, the clearance at the reduced ends increasing axially respectively towards the respective ends of the skirt; and wherein the regulating strips are embedded in body material of the piston only at their ends, for the remainder they abut along the inner surface of the skirt at least on their external circumference and they have no contact with the body material at least on their internal circumference.     
     
     
       2. A plunger piston according to claim 1, wherein a minimum diameter of the reduced ends of the skirt is less than the maximum diameter of the skirt by 0.1 mm under operating conditions. 
     
     
       3. A plunger piston according to claim 1, wherein only one regulating strip is arranged on each side of the boss bores, each strip having an axial dimension of between 5% and 25% of the maximum piston diameter. 
     
     
       4. A plunger piston according to claim 1, wherein the regulating strips extend circumferentially into a respective hub about the bosses. 
     
     
       5. A plunger piston according to claim 1, wherein the regulating strips extend circumferentially over a range of from 90 to 140 degrees. 
     
     
       6. A plunger piston according to claim 1, wherein the piston has the following dimensional relationships (H/D)=25-50% (T/D)=45-80% (A/D)=20-50% (s/D)=5-25% where   D=piston diameter   H=dimension from the gudgeon pin boss bore axis to an upper surface of the piston head,   T=distance between radially externally situated boss surfaces,   A=skirt length in a region of intersection of the bearing surface with the plane of oscillation of the connecting rod   s=total axial strip height.